This is a self-skipping generator: the output from the generator
at each step is fed back into the skipstate input (so for every output
bit of one, the next bit is skipped).

I am wary of these sorts of simple feedbacks. The generator's state
has too simple a relation to the feedback, and I don't trust it. You know
the next state will be skipped when the output is 1, which facilitates a
known-plaintext attack. This seems highly insecure.

This is a mutual skipstate generator. Each generator controls the skip
input of the other, and the output of the device is the the exclusive or
of the two outputs.

I think this one is nicer; regardless of the output you can't tell
exactly whether or not states were skipped and in which generator.

Since a skipstate generator is an inline generator, more complex
generators can be formed using it. Check out the
Tom7-inline-bridge device, for instance.